The present invention relates to motorboats with inboard engines, and more particularly to a safety device for automatically operating a ventilation fan for an engine compartment until the boat has reached a speed at which natural ventilation of the engine compartment is sufficient for safety against combustible mixtures of fuel fumes and air.
Fires in the engine compartments and bilge areas of motorboats powered by gasoline engines annually cause thousands of documented boat fires. It is suspected that the number of documented fires from such causes represents only a small minority of the actual occurrences.
Most of the fires in engine compartments result from ignition of accumulated fuel fumes. The fumes from even a small amount of fuel leakage into the bilges and engine compartment of a motorboat can result in a highly explosive mixture which is heavier than clean air and therefore remains in the bilge areas and is likely to remain in the engine compartment of a motorboat while it rests alongside a pier. Any spark, such as a spark which may occur within a starter motor, may be sufficient to ignite the explosive gas mixture, with disastrous results.
In order to avoid fires started in fuel fumes it is commonly accepted procedure to start a ventilation fan in operation prior to first starting the engine of such a boat. However, should there be an active leak of fuel from a carburetor, a fuel line, or other source, fumes may continue to accumulate during operation of the engine, so long as the boat lies at rest or its motion through the water does not result in sufficient flow of ambient air to flush fumes from the engine compartment and other low-lying areas within the hull of the boat. Fortunately, so long as the boat is moving through the water at an ample speed, fumes are less likely to accumulate undiscovered as an explosive mixture in dangerous quantities in locations where sparks are likely to be present. So long as a properly designed motorboat travels forward at an adequate speed, there exists a natural convection flow of air through the engine compartment to remove hazardous vapors.
What is not provided for by the prior art, however, are the many situations where there is no forward movement of the boat, yet the engine is running and the engine compartment ventilation system has been turned off. In such situations, the operator of a motorboat is likely not to turn on the ventilation fan, and combustible vapors can then accumulate in quantities sufficient to create explosive or flammable mixtures of fumes with the air.
In the past, various attempts have been made to avoid the risk of explosion and fire in motorboats with inboard engines. Devices have been disclosed, as in Yoshikawa U.S. Pat. No. 3,948,202 and Haden U.S. Pat. No. 3,789,231 for turning on an exhaust fan in a boat in response to sensing that vapors exceed a predetermined concentration in a particular enclosed area of a boat. Other devices have provided for delay in activation of starting and ignition circuits of motorboat engines until ventilating fans have been operated for a time, as disclosed in Doench U.S. Pat. No. 3,951,091.
Van Ranst U.S. Pat. No. 3,315,584, Kercheval, et al. U.S. Pat. No. 4,134,112, and Hoffman, Jr. U.S. Pat. No. 3,489,912 disclose devices which include vapor detectors used together with devices which control operation of the starter or engine of a motorboat at least partially in response to sensing the presence of flammable or explosive gas.
While such prior art devices may be helpful in preventing fires, they depend upon detection of a condition which may already be dangerous, rather than providing a way to prevent accumulation of dangerous fumes in the engine compartment of a boat.
Japanese patent No. 59-38109 discloses control of ventilation fans for the passenger compartment of an automobile, in response to stoppage or slow movement, but the invention appears to be related to ventilation for comfort, rather than having any relationship to safety from ignition of fuel fumes.
What is needed, then, is a method and apparatus for preventing accumulation of dangerous fumes at all times during operation of an inboard engine of a motorboat, rather than only prior to initial start-up of the engine.